1. Field of the Invention
The present invention relates to gas burner apparatus and methods for burning fuel gas-air mixtures whereby flue gases having low NOx content are produced.
2. Description of the Prior Art
Emission standards are continuously being imposed by governmental authorities which limit the quantities of gaseous pollutants such as oxides of nitrogen (NOx) which can be emitted into the atmosphere. Such standards have led to the development of various improved gas burner designs which lower the production of NOx and other polluting gases. For example, methods and apparatus have been developed wherein all of the air and some of the fuel is burned in a first zone and the remaining fuel is burned in a second zone. In this staged fuel approach, an excess of air in the first zone acts as a diluent which lowers the temperature of the burning gases and thereby reduces the formation of NOx. Other methods and apparatus have been developed wherein flue gases are combined with fuel gas and/or fuel gas-air mixtures to dilute the mixtures and lower their combustion temperatures and the formation of NOx.
While the above described prior art methods and burner apparatus for producing flue gases having low NOx content have achieved varying degrees of success, there still remains a need for improvement in gas burner apparatus and methods of burning fuel gas whereby simple economical burner apparatus is utilized and low NOx content flue gases are produced. Further, the burner apparatus utilized heretofore to carry out the above described methods have generally been large, produce flames of long length and have low turn down ratios.
Thus, there are needs for improved burner apparatus and methods which produce low NOx content flue gases and the burner apparatus are compact, have short flame lengths and have high turn down ratios.